A conventional solid-state laser apparatus will be described referring to FIGS. 5 to 7.
FIG. 5 is a schematic diagram showing a conventional solid-state laser apparatus, and the light path of a laser beam emitted by the solid-state laser apparatus.
In FIG. 5, reference number 1 denotes an oscillator head; 2, a resonator; 3, a partial reflector; 4, a full reflector; 5, an LD module, which is an excitation light source; 6, a laser medium, which is an excitation medium; 7, a case (hereinafter, where needed, referred to as a “cavity”) in which the LD module 5 and the laser medium 6 are stored; 8, a laser beam emitted by the resonator 2; 9, an expansion lens; 10, a collimating lens; 11, a beam shutter; 20, a condenser lens; 21, a fiber holder; 22, an optical fiber entrance section, formed of the condenser lens 20 and the fiber holder 21; 23, an optical fiber; and 24, a machining head.
The laser oscillation operation will now be described. Inside the resonator 2 in FIG. 5, the laser medium 6 is excited by excitation light emitted by the LD module 5, and laser oscillation is begun using the partial reflector 3 and the full reflector 4, provided so that they sandwich the laser medium 6. The laser beam 8, emitted by the resonator 2, is expanded while passing through the expansion lens 9, and is changed, by passing through the collimating lens 10 and the beam shutter 11, to parallel laser beams 8 that enter the optical fiber entrance section 22.
The parallel laser beams 8 incident to the optical fiber entrance section 22 are condensed by the condenser lens 20 of the optical fiber entrance section 22, and enter an end of the optical fiber 23, held by the fiber holder 21, as a condensed beam that is transmitted inside the optical fiber 23.
The laser beam 8, after passing through the optical fiber 23, is output at the other end of the optical fiber 23, which is connected to the machining head 24, and is used for a machining process.
FIG. 6 is a schematic diagram showing the structure of the cavity 7, and FIG. 7 is a schematic diagram showing the structure of the LD module 5. In FIG. 6, (a) is a front view and (b) is a side view. Reference numeral 33 denotes a condenser formed of a reflecting member; 34, a gap formed in the condenser 33; 35, a pipe; and 36, a pipe joint, through which cooling water, fed by a cooling water supply device (not shown), flows and cools the LD module 5 and the laser medium 6.
Reference numeral 40 denotes a laser diode (hereinafter, when needed, referred to as an “LD”) for generating excitation light; and 41 denotes a heat sink for holding and cooling the LD 40. The heat sink 41, to which the pipe joint 36 and wiring line 43a are connected, is designed so that cooling water, supplied by the pipe 35, flows into and through it. An electrode 42, connected to a wiring line 43b, supplies power provided by a laser diode power source (not shown).
Since the characteristic of the LD 40, especially a wavelength important to the YAG excitation, is changed as the temperature of the cooling water, which cools the LD module 5, is adjusted to maintain a constant temperature. For the LD 40, the excitation efficiency is improved as the temperature of the water is reduced; however, while taking into account the dew condensation, which occurs in the cooling system at high temperatures, the temperature set for the water tends to fall within a range of from 20° C. to 25° C.
The operation of the LD module 5 will now be described. When power is supplied by the laser diode power source to the LD 40 through the electrode 42, the LD 40 emits light and also generates heat. The heat that is generated is transmitted to the heat sink 41, and is lowered by the cooling water that flows across the heat sink 41.
The emitted LD light passes through the gap 34 of the condenser 33 in FIG. 6, and is transmitted to the internal cylindrical portion of the condenser 33. Then, the light passes through a flow tube (not shown) and is absorbed by the laser medium 6, and excites the laser medium 6. Subsequently, after the laser medium 6 has been excited, the laser beam is oscillated.
Since upon the absorption of the LD light the laser medium 6 not only begins laser oscillation but also generates heat, the laser medium 6 is cooled by the cooling water that flows between the flow tube and the laser medium 6.
The interior of the cavity 7 constitutes a semi-closed structure for blocking the entry of dust and to thus prevent the dust from being attached to the LD 40. However, the entry into the cavity 7 of water contained in the atmosphere is inevitable. Further, for the solid-state laser apparatus, unlike the case for a gas laser apparatus, it is not always necessary for the cavity 7 to substantially be closed in the vacuum state, and this is not normally performed because of the cost, etc. Therefore, if the ambient atmosphere contains a large amount of water, water gradually enters the cavity 7 that has been assembled. Further, when the cooling water slightly permeates at the cooling water pipe in the cavity 7, the amount of water in the cavity 7 is increased even more.
When the air temperature in the cavity 7 is changed, the relative humidity is changed because the absolute humidity is substantially constant. When the temperature is reduced, the relative humidity is increased, so that when the apparatus is activated at a high temperature or is halted at a low temperature, the dew condensation will occur at the parts surrounding the LD 40, such as at the heat sink 41 and a sub-mounting portion (not shown), and the LD 40.
When the dew condensation occurs at the LD 40, the light emission portion of the LD 40 becomes dirty easily. And as a result, the light emission portion becomes dusty and stained due to the dirt, and the output of the LD 40 is deteriorated or destabilized. Further, the dew condensation at the heat sink 41 and the sub-mounting portion causes corrosion at those locations. Then, within an extended period of time, a saprophagous organism covers the light emission portion of the LD 40, causing the output to be deteriorated, or after this organism has grown, a short-circuit can be caused that disables the emission of light by the LD 40. Accordingly, when the output of the LD 40 is reduced, the laser output of the resonator 2 is reduced.
As is described above, in the conventional solid-state laser apparatus, the dew condensation in the cavity 7 causes not only a reduction in the output and the destabilization of the LD 40, but also a reduction in and the destabilization of the output of the oscillated laser beam. Thus, a problem has arisen in that the dew condensation within the cavity 7, including the LD 40, must be prevented.